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Don't crash SMTP client when TLS is optional and we failed to handshake #258

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Mar 25, 2021
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Don't crash SMTP client when TLS is optional and we failed to handshake #258

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38 changes: 36 additions & 2 deletions src/gen_smtp_client.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -296,7 +296,7 @@ try_smtp_sessions([{_Distance, Host} | _Tail] = Hosts, Options, RetryList) ->
end.

-spec handle_smtp_throw(failure(), [{non_neg_integer(), smtp_host()}], options(), list()) ->
smtp_client_socket() |
{ok, smtp_client_socket()} |
smtp_session_error().
handle_smtp_throw({permanent_failure, Message}, [{_Distance, Host} | _Tail], _Options, _RetryList) ->
% permanent failure means no retries, and don't even continue with other hosts
Expand All @@ -307,7 +307,7 @@ handle_smtp_throw({temporary_failure, tls_failed}, [{_Distance, Host} | _Tail] =
if_available ->
NoTLSOptions = [{tls,never} | proplists:delete(tls, Options)],
try open_smtp_session(Host, NoTLSOptions) of
Res -> Res
Res -> {ok, Res}
catch
throw:FailMsg ->
handle_smtp_throw(FailMsg, Hosts, Options, RetryList)
Expand Down Expand Up @@ -1093,6 +1093,40 @@ session_start_test_() ->
end
}
end,
fun({ListenSock}) ->
{"Transaction with TLS advertised, but broken, should be restarted without TLS, if allowed",
fun() ->
Options = [{relay, "localhost"}, {port, 9876}, {hostname, <<"testing">>}, {tls, if_available}],
{ok, _Pid} = send({<<"[email protected]">>, [<<"[email protected]">>], <<"hello world">>}, Options),
{ok, X} = smtp_socket:accept(ListenSock, 1000),
smtp_socket:send(X, "220 Some banner\r\n"),
?assertMatch({ok, "EHLO testing\r\n"}, smtp_socket:recv(X, 0, 1000)),
smtp_socket:send(X, "250-hostname\r\n250 STARTTLS\r\n"),
?assertMatch({ok, "STARTTLS\r\n"}, smtp_socket:recv(X, 0, 1000)),
smtp_socket:send(X, "220 ok\r\n"),
%% Now, send some invalid data instead of TLS handshake and close the socket
{ok, [22, V1, V2 | _]} = smtp_socket:recv(X, 0, 1000),
smtp_socket:send(X, [22, V1, V2, 0, 0]),
smtp_socket:close(X),
%% Client would make another attempt to connect, without TLS
{ok, Y} = smtp_socket:accept(ListenSock, 1000),
smtp_socket:send(Y, "220 Some banner\r\n"),
?assertMatch({ok, "EHLO testing\r\n"}, smtp_socket:recv(Y, 0, 1000)),
smtp_socket:send(Y, "250-hostname\r\n250 STARTTLS\r\n"),
?assertMatch({ok, "MAIL FROM:<[email protected]>\r\n"}, smtp_socket:recv(Y, 0, 1000)),
smtp_socket:send(Y, "250 ok\r\n"),
?assertMatch({ok, "RCPT TO:<[email protected]>\r\n"}, smtp_socket:recv(Y, 0, 1000)),
smtp_socket:send(Y, "250 ok\r\n"),
?assertMatch({ok, "DATA\r\n"}, smtp_socket:recv(Y, 0, 1000)),
smtp_socket:send(Y, "354 ok\r\n"),
?assertMatch({ok, "hello world\r\n"}, smtp_socket:recv(Y, 0, 1000)),
?assertMatch({ok, ".\r\n"}, smtp_socket:recv(Y, 0, 1000)),
smtp_socket:send(Y, "250 ok\r\n"),
?assertMatch({ok, "QUIT\r\n"}, smtp_socket:recv(Y, 0, 1000)),
ok
end
}
end,

fun({ListenSock}) ->
{"AUTH PLAIN should work",
Expand Down